Common Pill Woodlouse

Armadillidium vulgare may reach up to a length of 18 millimetres (11⁄16 in), and are capable of rolling into a ball when disturbed. This ability, along with its general appearance, gives it the name pill-bug. This may create the potential for confusion with pill millipedes such as Glomeris marginata. It can be distinguished from Armadillidium nasatum and Armadillidium depressum by the gap that A. nasatum and A. depressum leave when rolling into a ball; A. vulgare does not leave such a gap.

The native distribution of A. vulgare ranges across Europe, especially in the Mediterranean Basin. Though, A. vulgare are exceptionally adaptable which have allowed them to spread worldwide in countries like the United States, Madagascar, Australia and South Africa. In North America, populations may reach up to 10,000 individuals per square metre (900 individuals per square foot). It is now one of the most abundant invertebrate species in California coastal grassland habitats. They are also anthropophilic, as man-made waste like cardboard can provide suitable habitats, making them one of the most widely distributed species of woodlouse.

The diet of A. vulgare is incredibly varied. Primarily, the species are detritivores primarily feeding on decomposing plant litter. However, they have also been shown to consume seeds (granivory), living plant matter, dead animal remains, fungi and dung. A. vulgare consumption of fungi in particular has shown to have regulatory impacts on the release of carbon dioxide (a greenhouse gas). since the fungi that the woodlouse consume create positive feedback loops via decomposition that warm up climates and ecosystems. The proliferation of pill bugs allow for fungi to be controlled within ecosystems. A. vulgare were also found to forage at higher rates at night with lower temperatures and higher relative humidity. In drier environments, A. vulgare were shown to spend more time sheltering as opposed to feeding or foraging because the exposure to drier air leads to rapid water loss and subsequent loss of body mass. The effects of climate change on decreased rainfall and increased drought threatens A. vulgare and their aversion to dry environments.